This invention relates to a closed loop control system. More particularly, it relates to such a system for controlling the flow of sinter out of an accumulating hopper.
In order to improve the operation of a blast furnace, fine ores, or fines, are screened from the ores to be supplied to the blast furnace. These fines are mixed with coke breeze, as well as small quantities of other materials well known in the art, and the resultant mixture is fed to a sintering machine where it is fused into larger size particles. This mixture is carried through the sintering machine on pallets, and the resultant coarser particles are subsequently dumped from these pellets, as discrete batches, onto a cooling conveyor, or cooler. After cooling, these batches of sinter are fed by conveyor belt to one of several blast furnaces.
It is desirable to feed a steady stream of sinter to a blast furnace. This, however, is complicated by several factors. As mentioned earlier, the sinter leaves both the sintering machine and the cooler in batches rather than as a continuous flow. In addition, the speed of the output from the sintering machine may increase or decrease temporarily due to the operating conditions of the sintering machine itself. As a further complicating factor, it is periodically necessary to stop the flow of sinter out of the sintering machine while the flow path of the sinter is changed from a conveyor belt leading to one blast furnace to another conveyor belt leading to another blast furnace.
In the past, a first accumulating hopper has been interposed between the feed means supplying the hot sinter to the cooler and the cooler itself. A second accumulating hopper has been interposed between the feed means supplying the cooled sinter to the conveyor belts leading to the blast furnace and the belts themselves. Both of these hoppers were provided with control systems that sensed the level of the material in the hopper. As the sensed level in a hopper varied from a preset reference level, an error signal was fed back to control the discharge feed rate from that hopper.
One problem that presented itself in this prior art system was that, as a result of the batch input into the system, an error signal was always present. This error signal oscillated about a reference level and prevented the control system from ever stabilizing.
It is an object of the present invention to provide a control system that maintains a fairly constant level in a hopper with a high degree of stabilization.
A second problem that presented itself in this prior art system was that relatively large error signals often occurred due to changes in the speed of the sinter machine, for example. No practical control system was available that functioned efficiently to control the hopper level despite both the relatively small changes due to the batch effect and also the relatively large changes due to speed changes in the sinter machine.
It is an object of the present invention to provide a control system that maintains a substantially constant level in an accumulating hopper despite both small and large changes in the rate of input of material into the accumulating hopper.